1. Technical Field
Technical field relates generally to radioactive sourcewires for treatment of diseases, and, more particularly, to a flexible sourcewire for use in radiation therapy after an angioplasty procedure in order to minimize the occurrence of restenosis.
2. Description of the Related Art
During or after the performance of a percutaneous transluminal angioplasty procedure to relieve a constriction within a patient""s vessel, it has been found beneficial to irradiate the site of the constriction to prevent reclosure or restenosis due to smooth muscle cell proliferation. Typically, a catheter having a blind lumen extending to a distal end thereof is advanced to the treatment site and a sourcewire having a radioactive tip is advanced to the treatment zone of the catheter adjacent the treatment site within the vessel. This is typically accomplished by connecting a proximal end of a catheter to a mechanism for advancing the sourcewire, such as an afterloader, and operating the afterloader to advance the sourcewire to the treatment site.
Commonly, in afterloaders, the sourcewire is substantially wound about a reel or spool with only the distal end, that containing the radioactive source, left in a straight or uncoiled position. The radioactive source is typically housed within a shielded container provided on the afterloader. In operating the afterloader, the sourcewire is unraveled off the reel and advanced through the catheter down the various narrow or tortuous pathways to reach the arteries and, in particular, the remote coronary arteries. Sourcewires may be repeatedly used over again until such time as the radioactive level of the radioactive source is of no further beneficial use.
During the repeated cycling of the sourcewire about the reel and through the catheter to reach the coronary arteries, the sourcewire is subjected to various stresses and strains along its length thereof. This may pose problems in particular sourcewire constructions which can result in cracking, buckling or kinking at various positions along the sourcewire. In one known sourcewire construction, the sourcewires are formed by having a full length tube with a substantially full length backbone wire affixed therein. The backbone wire terminates short of the distal end of the tube to define a cavity for receipt of a radioactive source or sources therein. The backbone wire construction of the radioactive sourcewire provides the advantage of allowing a relatively long treatment zone to be provided by the tube defining the cavity at a distal end thereof. Alternatively, sourcewires formed from an entirely solid wire having a drilled distal end for receipt of a radioactive core are known. The solid wire construction is less prone to damage from repeated cycling. However, when constructing sourcewires of relatively small diameters, less than 0.014 of an inch, it becomes difficult to drill a cavity into this sourcewire of sufficient length to accommodate the desired longer radioactive sources.
Thus, there exists a need for a radioactive sourcewire combining the strength and flexibility of a substantially solid wire along the predominant length thereof as well as having a tubular construction at a distalmost end to accommodate varying lengths of radioactive sources.
There is provided a radioactive sourcewire having an elongated flexible and substantially solid wire and a tube extending from a distal end of the wire. A radioactive source may be provided in the cavity defined by the tube and the distal end of the tube sealed to prevent release of the radioactive source. Preferably, both the wire and tube are formed of a shaped memory alloy such as a nickel titanium alloy tor increased flexibility. Various embodiments and methods relating to the juncture of the solid wire and tube are disclosed herein. In the disclosed embodiments, the wire is formed with a flush distal face which is substantially perpendicular to longitudinal axis of the wire. Similarly, the tube is formed with a flush proximal face which is substantially perpendicular to the longitudinal axis of the tube. Various constructions are provided wherein the flush face of the wire is abutted against the flush face of the tube and the two are permanently affixed or secured together.
In a first embodiment, the wire is affixed to the tube by bringing the two flush bases into abutting relationship and providing a circumferential weld or other means of affixing the wire to the tube. The tube may then be sealed at the distal end by means of a plug affixed thereto or the distal end of the tube, as will be common in all embodiments, may be ground flush or welded closed and then ground to provide a smooth surface.
In an alternative embodiment, a connector or rod is formed projecting from the distal flush face of the wire and is configured to frictionally engage the interior of the tube. The rod does not extend the full length of the tube but terminates short of the distal end of the tube to provide a cavity for receipt of the radioactive material.
In a further alternative embodiment, a rod is initially inserted into the tube to provide a substantially flush face across the proximal end of the tube. The flush face of the proximal end of the tube is then mated as above with the flush face of the wire and the two secured by known methods.
In yet a further alternative embodiment of the disclosed sourcewire, the distal end face of the wire is drilled to form a bore for receipt of one end of the rod. As with the above embodiment, the distal end of the rod is inserted into the proximal end of the tube and the entire assembly is welded together.
Notably, where the tube is to be of a length greater than approximately 3 centimeters and less than approximately 20 centimeters, the rod may extend a significant distance into the tube. The rod may be tapered to provide flexibility along its length within the tube and include a rounded distal end which substantially seals the tube. The radioactive source would be provided distal of the rounded end and the distal end of the tube sealed as with other embodiments.
In a further alternative embodiment, a proximal end of the tube is welded shut and then ground shut, providing a flush face for abutment and a fixation to the flush surface of the wire. This provides an added advantage in assuring some structural rigidity to the proximal end of the tube when it is mated to the wire without the use of connectors. In further alternative embodiments, intermediate connectors may be provided between the wire and the tube. Specifically, the connectors may include male/female ends for receipt of a ground down male end of the wire and insertion into the female end of the tube, or alternatively, as above, the wire may be drilled to form a substantial bore in a distal end and the connector includes two male ends for fitting into the wire and into the tube.
In an alternative construction of the distalmost end of the sourcewire, a spring coil is formed at the distal end of the tube either on the plug or in combination with the welded distal end of the tube. The spring coil facilitates tracking of the sourcewire through a catheter and acts as a shock absorber to prevent the sourcewire from damaging the internal distal end of the blind lumen.
In an alternative construction and the method of forming a radioactive sourcewire, a core material is positioned within a tube and the distal end of the tube sealed by welding or with a plug as disclosed herein. A second weld or plug is provided internal to the tube adjacent the core to encapsulate the core within the tube to form a distal end assembly of a sourcewire. The distal end assembly of the sourcewire is then subject to irradiation in a nuclear reactor to render the core radioactive. After the core has been made radioactive, the distal end assembly may be affixed to a solid elongate wire in accordance with the various constructions herein.
In an alternative construction of a sourcewire, a flush proximal end of a tube is welded to a flush distal end of an elongate driving wire and an overlay tube is affixed to the outer surfaces of the proximal end of the tube and the distal end of the driving wire. Preferably, the overlay tube is affixed by means of spot welds at various locations. Additionally, an internal backbone wire may be provided in the proximal portion of the tube and secured therein by internal spot welds.
In another embodiment of the sourcewire, the sourcewire is formed by providing a flexible solid or driving wire having a predetermined outer diameter and welding a flush distal end of the driving wire to a tube having a predetermined outer diameter less than the diameter of the wire. The differences in diameters provides a natural step that, when welded, epoxyed or otherwise secured, provides a smooth tapered transition without protrusion about the juncture of the wire in the tube. Preferably, a rod extending from the distal end of the wire is configured for securement within the tube. Core material is inserted into the tube and the distal end of the tube is sealed by means of a weld or plug.
In a particular method of forming a distal end of the sourcewire, a tube is provided with a section of core material therein. The tube has an open distal end. The open distal end of the tube is welded closed with a predetermined amount of weld material to seal the distal end of the tube. Thereafter, the weld material is ground to form a tapered distal tip on the sourcewire.